The present invention relates to a laser ablation device for forming a thin film by means of a short wavelength laser light, and more particularly, to a laser ablation device for forming a soft magnetic thin film of an oxide.
A conventional example of a laser ablation device for forming an oxide thin film using a short wavelength laser light is described in Japanese Journal of Applied Physics, vol. 27 (1988) by S. Komuro et al. The constitution of the prior art will be described with reference to FIG. 6.
The conventional laser ablation device for forming a thin film includes a target holder 41' for holding a target 41 of the sintered body of Ni-Zn-ferrite as an oxide film forming material, and a substrate holder 42 (holder for an object on which a film is to be formed) confronting the target holder 41' to hold a substrate 43 (the object on which a film is to be formed) in a vacuum chamber 40. The vacuum chamber 40 has a discharging device 49, a gas introduction port 48, and a light-transmittable window 47. A short wavelength laser light 45 having a wavelength of 532 nm, which is the second higher harmonic laser light of a YAG laser 44 performing Q switching of a visible light and placed outside the vacuum chamber 40, is condensed by an optical system 46 and irradiates the target 41 through the light-transmittable window 47. A heater 42' is built into the substrate holder 42 to heat the substrate 43 to a predetermined temperature.
The operation of the above-described laser ablation device will be discussed with reference to FIG. 6.
In FIG. 6, after the vacuum chamber 40 is evacuated by the discharging device 49, O.sub.2 gas or N.sub.2 O gas is introduced into the chamber 40 from the gas introduction port 48. The short wavelength laser light 45 irradiates the target 41. As a result, ablated particles are projected from the sintered body of Ni-Zn-ferrite constituting the target 41 owing to the energy of the short wavelength laser light, and a thin film of Ni-Zn-ferrite is formed on the substrate 43 held by the substrate holder 42 opposed to the target 41.
At the time the thin film is formed, since the substrate 43 is heated to a predetermined temperature by the built-in heater 42' of the substrate holder 42, and an oxidating gas such as O.sub.2 gas or N.sub.2 O gas is introduced in the chamber 40 from the gas introduction port 48, the Ni-Zn-ferrite thin film formed on the substrate 43 reacts with the oxygen, whereby the oxygen deficiency of the Ni-Zn-ferrite thin film is reduced.
However, for an oxide of many components such as those represented by Ni-Zn-ferrite, the oxygen reacts only to a little extent and the oxygen deficiency of the thin film cannot be sufficiently reduced. Therefore, the prior art is capable of forming a thin film of high coercive force only.
In the event that the thin film of Ni-Zn-ferrite or the like formed by the conventional laser ablation device is to be employed as a soft magnetic film of low coercive force, it becomes necessary to impart characteristics to the film by which the film will exhibit lower coercive force. More specifically, the oxidation state of the thin film (valence, etc.) must be precisely adjusted to thereby sufficiently reduce the oxygen deficiency. For this purpose, the substrate 43 with the thin film has been conventionally heated under an oxidation atmosphere at high temperatures (for example, 800.degree. C. or higher) and annealed for several hours. Therefore, a large number of processing steps are needed accompanied by the cost associated therewith.
Moreover, the above-mentioned annealing at high temperatures cannot be applied to a thin film head because the material of the head cannot withstand temperatures higher than 350.degree. C. In other words, the conventional laser ablation device is useless when a thin film head is to be manufactured.